Consequences of anatomic changes and respiratory motion on radiation dose distributions in conformal radiotherapy for locally advanced non-small-cell lung cancer.
OBJECTIVE
To determine the effect of interfractional changes in anatomy on the target and normal tissue dose distributions during course of radiotherapy in non-small-cell lung cancer patients.


METHODS
Weekly respiration-correlated four-dimensional computed tomography scans were acquired for 10 patients. Original beam arrangements from conventional and inverse treatment plans were transferred into each of the weekly four-dimensional computed tomography data sets, and the dose distributions were recalculated. Dosimetric changes to the target volumes and relevant normal structures relative to the baseline treatment plans were analyzed by dose-volume histograms.


RESULTS
The overall difference in the mean +/- standard deviation of the doses to 95% of the planning target volume and internal target volume between the initial and weekly treatment plans was -11.9% +/- 12.1% and -2.5% +/- 3.9%, respectively. The mean +/- standard deviation change in the internal target volume receiving 95% of the prescribed dose was -2.3% +/- 4.1%. The overall differences in the mean +/- standard deviation between the initial and weekly treatment plans was 3.1% +/- 6.8% for the total lung volume exceeding 20 Gy, 2.2% +/- 4.8% for mean total lung dose, and 34.3% +/- 43.0% for the spinal cord maximal dose.


CONCLUSIONS
Serial four-dimensional computed tomography scans provided useful anatomic information and dosimetric changes during radiotherapy. Although the observed dosimetric variations were small, on average, the interfractional changes in tumor volume, mobility, and patient setup was sometimes associated with dramatic dosimetric consequences. Therefore, for locally advanced lung cancer patients, efforts to include image-guided treatment and to perform repeated imaging during the treatment course are recommended.
Britton
Keith R
KR
Department of Radiation Physics, Division of Radiation Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX, USA.
Starkschall
George
G
Liu
Helen
H
Chang
Joe Y
JY
Bilton
Stephen
S
Ezhil
Muthuveni
M
John-Baptiste
Sandra
S
Kantor
Michael
M
Cox
James D
JD
Komaki
Ritsuko
R
Mohan
Radhe
R
D000368:Aged; D000369:Aged, 80 and over; D001822:Body Burden; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D009038:Motion; D011835:Radiation Protection / Q000379:methods; D011859:Radiography; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012062:Relative Biological Effectiveness; D015656:Respiratory Mechanics